1. Field of the Invention
The present invention relates to a meter for measuring mass flow rate and, in particular, to a meter for measuring mass flow rate by vibrating a conduit that carries the material whose flow rate is being measured.
2. Description of the Prior Art
This invention relates to a dynamic vibratory meter for measuring the mass of material flowing therethrough, including liquids, gases, slurries and other fluent material, and in particular where the measurement is accomplished by vibration of an unobstructed conduit. The major advantages of such meters are that they measure the mass flow rate directly and that the conduit need not contain any moving parts or other obstructions. Such meters are particularly useful in the food and chemical process industries. They can also find application in metering highly compressed or liquified gases.
Various meters have been described in the past 35 years that measure mass flow rate by the transverse vibration of some form of conduit, including discontinuous tubes. The most pertinent art prior to this invention known to the applicant that involves continuous tubes is: Roth, U.S. Pat. No. 2,865,201; Sipin, U.S. Pat. No. 3,329,019; Sipin, U.S. Pat. No. 3,355,944; Cox et al., U.S. Pat. No. 4,127,028; Smith, U.S. Pat. No. 4,187,721 and Smith, U.S. Pat. No. 4,252,028.
Roth shows a gyroscopic mass flow meter in which fluid flows through a circular conduit of approximately 360.degree., as an analog of a rotating gyroscope wheel, which is oscillated about a central axis.
In U.S. Pat. No. 3,329,019, Sipin shows a single straight conduit which is flexed under a forced transverse vibration and the torque exerted by the conduit about a torque axis orthogonal to both the flow path and the direction of vibration is sensed as an indication of mass flow rate. This torque is produced by opposing transverse forces in the inlet and outlet sections of the conduit produced by transverse vibration of the mass flow.
Since the transverse vibrational velocity due to flexure of a straight tube can be limited, Sipin, in U.S. Pat. No. 3,355,944 shows the vibration of a curved tube in order to increase the vibrational velocity and the magnitude of the force couple. The orthogonal relationships among torque, vibration and flow are the same as for the straight tube. The tube is limited to a bend of 180 degrees or less to minimize or eliminate reversals in flow direction. Cox et al. show two parallel U-shaped tubes having the same fluid flow through both of them and vibrating in opposite directions. Differential motion is sensed as an indication of mass flow rate. The inlet and outlet are parallel and clamped in a support, the fluid flowing in opposite directions through them. The U-shaped tubes contain bent portions said to increase the Coriolis force moment arms.
In U.S. Pat. No. 4,187,721 Smith shows a U-shaped conduit mounted in a cantilevered manner with the conduit oscillating means mounted on a separate arm having a natural frequency substantially that of the U-shaped tube. The inlet and outlet are also parallel and clamped in a support, the fluid flowing in opposite direction through them.
In U.S. Pat. No. 4,252,028 Smith shows multiple parallel U-tubes oscillated together to measure combined flow of more than one fluid stream.